Unit Test Base

TestBase.cs

	public class TestBase
	{
		private readonly ConcurrentDictionary<Type, object> _dependencies = new ConcurrentDictionary<Type, object>();

		/// <summary>
		/// Gets the substitute matching the provided type from the dependency list
		/// </summary>
		/// <typeparam name="T">The type of substitute to match</typeparam>
		/// <returns>The substitute matching the provided type</returns>
		public T GetSubstitute<T>()
		{
			return (T) GetSubstitute(typeof(T));
		}

		/// <summary>
		/// Gets the substitute matching the provided type from the dependency list
		/// </summary>
		/// <param name="t">The type of substitute to match</param>
		/// <returns>The substitute matching the provided type</returns>
		public object GetSubstitute(Type t)
		{
			object obj;
			if (_dependencies.TryGetValue(t, out obj))
				return obj;

			obj = AddDependency(t);
			if (obj == null)
				throw new NullReferenceException($"{t} was not found in the dependency list");

			return obj;
		}

		/// <summary>
		/// Registers an implementation of the provided type with the dependency list
		/// </summary>
		/// <typeparam name="T">The type to register</typeparam>
		/// <param name="instance">The instance of the provided type to register</param>
		public void Register<T>(object instance)
		{
			_dependencies.AddOrUpdate(typeof(T), instance, (k, v) => instance);
		}

		/// <summary>
		/// Creates an instance of the provided type, resolving or creating substitutions for its dependencies from the dependency list.
		/// </summary>
		/// <typeparam name="T">The type of instance to create</typeparam>
		/// <returns>An instance of the provided type</returns>
		public T CreateInstance<T>()
		{
			var ctor = typeof(T).GetConstructors().OrderByDescending(c => c.GetParameters()).FirstOrDefault();
			if (ctor == null)
				throw new NullReferenceException("Unable to determine the constructor to use");

			object[] parameters = ctor.GetParameters().Select(p => GetSubstitute(p.ParameterType)).ToArray();

			object instance = ctor.Invoke(parameters.ToArray());
			return (T) instance;
		}

		/// <summary>
		/// Adds the dependency to the dependency list
		/// </summary>
		/// <param name="t">The type to add</param>
		/// <returns>The substitute object</returns>
		private object AddDependency(Type t)
		{
			var sub = Substitute.For(new[]{t}, new object[] { });
			_dependencies.AddOrUpdate(t, sub, (k, v) => sub);			
			return sub;
		}
	}